Contracting pre-slice flow distributor for papermaking machine headbox

ABSTRACT

An inlet for a papermaking machine characterized particularly by a stationary flow distributor immediately preceding the slice within the headbox. The distributor has an overall contracting dimension from the inlet to the outlet and is arranged to provide initially small scale turbulent mixing to attain universal fiber orientation followed by an expanding stilling section in which some turbulence is dissipated so that stock is discharged from the slice onto a forming wire with a controlled level of small scale agitation and minimum fiber alignment. The distributor has an inlet face remote from the slice which is convex in shape and a downstream outlet face which is arcuate in shape in the same sense as the inlet face. Each passageway connecting an inlet opening in the inlet face with an outlet port in the outlet face gradually widens toward the outlet port, and each passage of a vertical row of passages extends toward the slice at a different angle which is less than 45*.

llnited States Patent Appel 51 Mar. 28, 1972 [54] CONTRACTING PRE-SLICE FLOW DISTRIBUTOR FOR PAPERMAKING MACHINE HEADBOX [72] Inventor: David W. Appel, Neenah, Wis.

[73] Assignee: Kimberly-Clark Corporation, Neenah,

Wis.

[22 Filed: Nov. 24, 1969 21 Appl.No.: 879,251

3,328,236 6/1967 Burgess et al. ..l62/343 X Primary Examiner -S. Leon Bashore Assistant Examines-R. H. Tushin Attorney-Daniel J. Hanlon, Jr. and Raymond J. Miller [5 7] ABSTRACT An inlet for a papermaking machine characterized particularly by a stationary flow distributor immediately preceding the slice within the headbox. The distributor has an overall contracting dimension from the inlet to the outlet and is arranged to provide initially small scale turbulent mixing to attain universal fiber orientation followed by an expanding stilling section in which some turbulence is dissipated so that stock is discharged from the slice onto a forming wire with a controlled level of small scale agitation and minimum fiber alignment. The distributor has an inlet face remote from the slice which is convex in shape and a downstream outlet face which is arcuate in shape in the same sense as the inlet face. Each passageway connecting an inlet opening in the inlet face with an outlet port in the outlet face gradually widens toward the outlet port, and each passage of a vertical row of passages extends toward the slice at a different angle which is less than 45.

3 Claims, 9 Drawing Figures P TENTEB MAR 2 8 I972 SHEET 1 BF 2 P'ATENTEDWBIQTZ 3,652,392

' sum 2 OF 2 FIG. 8 FIG. 6 FIG.?

FIG. 9

CONTRACTING PRE-SLICE FLOW DISTRIBUTOR FOR. PAPERMAKING MACHINE IIEADBOX BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to papermaking machines and, more particularly, to stock inlets for such machines. More specifically, the invention is directed to a stock inlet having an improved stock distributor through which the stock is directed to the slice and ejected onto a forming wire.

2. The Invention With Relation to the Prior Art The inlet of a paper machine commonly is intended to receive a flow of a dilute paper stock from a pumping system and to convert the flow to a homogeneous suspension, evenly spread in velocity and direction upon the papermaking wire. It is necessary to accomplish this in order to avoid undesirable variations in the properties of the finished paper; these variations may occur, for example, in basis weight profile, sheet streaks, light or sparse fiber areas, and sheet strength, particularly low strength transversely of the sheet.

One usual approach to flow control is the inclusion of an apertured distributor roll preceding the slice. Such roll, however, itself contributes to some non-uniforrnities, and streakiness frequently occurs in the sheet product, the result of eddies which pass through the roll or wakes created behind the roll in its rotation. It is to be noted also that distributor rolls have about 40 to 50 percent open area, usually constituted by drilled holes. At less than about 40 to 50 percent open area, flow through tends to be unstable but at more than about 50 percent open rolls are impractical to build. Also, with large open areas in the roll, those disturbances and non-uniformities which may exist in an approach flow pass on through the distributor. Additionally, distributor rolls are particularly ineffective in reducing cross-components of velocity so that other equipment must be included for this purpose.

Stationary tubular distributors are known and currently employed. This type of distributor has long slender or narrow passages which provide against transverse components of velocity in the region of the slice and the opening entrance area is advantageously in the range of about to percent of the face area, thereby providing relatively high entrance velocities to a pulp slurry. Also, an order of magnitude higher head loss occurs in comparison to a distributor roll arrangement.

l have found that significantly improved results as to uniformity of flow delivered to the forming wire and as to the quality of paper sheet formed may be attained by providing a particular stationary and tubular distributor preceding the slice and eliminating the distributor roll. The tubular distributor, for my purposes:

l. is a contracting distributor, that is, it has a large upstream inlet face, a small downstream outlet face, and an array of passages connecting the faces;

2. has wide land areas on the upstream face (80 to 90 per- 6. with the proportions of tubular distributor described total head loss through the distributor section is usually 25 to 50 percent of the velocity head at the slice and, therefore, headbox heads employing the distributor are 1.25 to 1.50 greater than is obtained with a distributor roll in the headbox.

By such generally described arrangement, a high velocity of flow is attained in the entrance of the distributor, a high level of turbulence but of small scale is generated in the small separation zone at the entrances of each tubular passage, the flow is then allowed to expand to fill the passage uniformly and then expanded further to the outlet of the'distributor to bring the mean velocity down to the magnitude of about 15 to 60 percent of the slice discharge velocity. This small stilling section allows some dissipation of the small, most intense turbulent eddies so that, as the flow leaves the slice, the free surface does not become excessively rough or break into a spray.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

FIG. 1 is a somewhat diagrammatic fragmentary side elevation of an inlet of a papermaking machine illustrating my improved arrangement;

FIG. 2 is an enlarged sectional view of the contracting distributor of FIG. 1 taken on line 2-2 of FIG. 3 particularly illustrating the arrangement of flow passages;

FIGS. 3 and 4 are respectively fragmentary right and left hand end views of the structure of FIG. 2;

FIG. 5 is a somewhat enlarged longitudinal sectional view of only a flow passage of a distributor similar to that shown in FIG. 2;

FIG. 6 is a sectional view of another embodiment of a tubular distributor in accordance with the invention;

FIGS. 7 and 8 are respectively right and left hand end views of the distributor of FIG. 6; and

cent of the face area), the land areas being large relative to the length of the fibers of the papermaking slurry to be employed with the distributor;

3. has means in the passages for forming jets of stock in an initial portion of the length of the passage, each passage widening to an outlet port closely positioned to the slice;

4. has passages over a final portion of their length which expand on linear tapers to the outlet face and are arranged to provide a minimum of wall thickness between adjacent passages to minimize the development of trailing wakes in the flow;

5. the distributor outlet face is close to the slice and there is minimum acceleration or contraction of the flow, the contraction in slurry flow depth from the outlet face of the distributor to the slice outlet being from about 3 inches to 1 inches and preferably the height of the outlet face of the distributor is no greater than 4 inches and, most suitably, between 2.5 and 3.5 inch; there is then achieved uniformity of fiow, the elimination of eddies and cross-flows, and there being provided a uniform level of small scale agitation; and

FIG. 9 is a fragmentary, enlarged sectional view of the right hand end of FIG. 6.

PREFERRED EMBODIMENTS OF THE INVENTION IN DETAIL Referring to the drawings more particularly, the numeral 1 in FIG. 1 generally designates a headbox of a papermaking machine having a bottom wall 2 and a transversely extending vertical baffle wall or darn 3 forming one side of a pond 4. The pond is, of course, otherwise suitably enclosed and has communication with a pumping system (not shown). The baffie wall 3 projects upwardly to the top 5 of the headbox from a tubular distributor designated generally at 6. The distributor has a relatively large arcuate upstream face 7 fronting on the pond 4 and a much smaller downstream and also arcuate face 8 opening toward the slice 9. A vertically extending baffle 10 extends upwardly to the headbox top 5 from the face 8 and cooperates with a downwardly angled wall 11 to bound the slurry issuing from the distributor to the slice. A breast roll 12 lies immediately below the slice. The bottom wall 2 of the headbox conveniently projects forwardly over the breast roll and terminates in a lip 13. A wire 14 passes around roll 12 and extends between lip 13 and the breast roll to receive the papermaking slurry.

In a preferred form illustrated in FIGS. 1 and 2, the tubular distributor upstream face 7 is convex to the pond 4 and has a plurality of circular entrance openings 15 to outlet ports 16. Passages which extend downwardly completely through the distributor communicating the openings and outlet ports have portions identified as 16a, 16b and 160. The openings 15 are positioned in vertical arrays on the face (FIG. 3) and are provided across the headbox in known manner to provide a width of distributor substantially equal to the wire 14 and headbox; openings 15 are separated by lands 17. The lands 17, that is, the closed spaces between openings 15, are provided to be large relative to the lengths of the fibers which form the slurry to be presented to the distributor. Also, the openings 15 are flush with the face 7 and lands 17. With wood pulp slurries the lands 17 are suitably k to 1% inch and the entrance openings 15 to the passages are conveniently about to 1 inch. Overall passage length is generally about 8 to about 16 inches and the downstream face of the distributor is between 5 and 12 inches away from the slice. The slurry velocity V,, at the openings 15 is usually relatively low. The passage portions 16a are long relative to the cross-sectional dimension of the entrance openings. Also, they are of the same configuration and size as the entrance openings. Thus, the initial passage length or zone designated at 16a is at least about four times the diameter of the entrance opening. In this zone 16a, the velocity ofthe pulp slurry is high, and much greater than that at V,,; the flow due to the abrupt presentation of the openings to the flow occurs as a small jet separating from the walls of the passage at the entrance l5 and forming a vena contracta" inside the entrance of the passage where the velocity is designated V The velocity V then decreases as the jet expands to fill the entire passage and attains a magnitude of V at the end of passage 16a. In the small annulus around the vena contracta" intense small-scale turbulence is generated due to the high shear between the jet and the surrounding fluid in the separation zone. The scale of this turbulence is small compared to the diameter of openings 15, and this works to disperse even the small clumps of fibers which enter a single passage. The passage at 1612 widens gradually as at 16c to the downstream face of the distributor and the velocity decreases to V allowing dissipation of a portion of the turbulence. Also in this preferred embodiment, the configuration of the passage changes to rectangular (FIG. 5) so that the outlet ports 16 of the distributor are rectangular in cross section. Additionally, the land areas 18 adjacent to the outlet ports 16 are thin and preferably minimal to avoid the introduction of disturbances which may arise from wakes, that is, the flows from adjacent passages merge smoothly to form a continuous flow without any additional turbulence or eddy formation.

The percentage of upstream face area of distributor 6 which is open as passages 15 is relatively small, advantageously about 10 to 20 percent of the face area. The percentage of open area at the downstream outlet ports is large, suitably 80 to 90 percent of the downstream face. These factors aid in controlling the mean velocities and, hence, control the turbulence imparted to the flowing stock, a turbulence which results in good fiber dispersion and tendency for orientation in all directions. This aids in attaining sheets with nearly the same properties in the machine and cross-machine directions. For example, sheets have been made with ratios of tensile strengths in the machine and cross-machine directions of less than 1:4 and as low as 1:1.

Importantly, the tendency of fibers to align in the direction of flow between the distributor outlet ports 16 and the slice is largely avoided by making the contraction of the flow small. There is then minimum acceleration of the flow. suitably, the flow depth is reduced from 3 inches, for example, at the outlet ports, to the slice opening which usually is less than 1 inch.

The passages in a vertical array (FIG. 2) each approach the slice at a different angle. The lowermost passage is very nearly in horizontal alignment with the slice to provide for convenient mounting of the distributor in existing headboxes. The uppermost passage, however, preferably is at an angle of less than 30 but may be as much as 45 to the slice. Too great an angle tends to cause air to be trapped in the distributor. The liquid head, however, at the slice will be substantially the same for liquid passing through each passage.

A further modification of the invention is illustrated in FIGS. 6-9 inclusive. The tubular distributor indicated by the numeral 20 in this instance has an upstream inlet face provided with entrance openings 23 and a smaller downstream outlet face 22. The inlet face, while having an overall arcuate configuration, is provided between openings 23 with land areas 27 which are each of arcuate nature and define the entrance openings 23 peripherally in such manner as to provide for smooth flow to such entrance openings. Each entrance opening 23 is communicated with an outlet 24 in the downstream outlet face 22. Further, a shoulder 25, as most clearly seen in the enlarged view of FIG. 9, is provided at each entrance opening. This shoulder 25 provides jet forming means for the slurry in the first zone adjacent the inlet opening; the shoulder serves to abruptly expand an inflowing stream and creates small scale turbulence similar to that created by the vena contracta of the embodiment of FIG. 1. Each passage immediately following the shoulder in the direction away from the inlet face is of uniform cross-sectional contour over a length at least about four times the height of the inlet opening of shoulder 15. Additionally, the passage widens gradually as indicated at 28 to provide for gradually decreasing turbulence. As in the prior embodiment, the land areas at the outlet face, as indicated at 26, are very narrow and, accordingly, there is little turbulence in the outflowing stream occasioned by the delivery of the flow to the slice. However, the small scale turbulence providing minimum fiber alignment and a small scale of agitation of the fibers in the slurry is preserved as the stock moves onto the wire.

As in the previously mentioned embodiment, the inlet openings as measured at shoulder 25 constitute between about 10 to 20 percent of the area of the arcuate inlet face, the land area of the outlet face is 20 percent or less of the total area, and the angle of approach of each passage to the slice area is greater as the inlet opening position is higher in the headbox.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myselfo the specific embodiments thereof except as defined in the appended claims.

I claim:

1. An inlet for a papermaking machine comprising a pond type headbox, a slice and a pre-slice flow distributor communicating with said slice for directing a flow of papermaking stock from said headbox to said slice, and distributor having relative to said slice a large upstream inlet face and vertically disposed inlet openings, said inlet face ofsaid distributor being convex on the side remote from said slice, a downstream outlet face small relative to said inlet face and larger than said slice and including outlet ports and a passage communicating each inlet opening with one outlet port, said downstream outlet face being arcuate in the same sense as the upstream inlet face, said upstream inlet face having relatively large land areas between said inlet openings and said downstream face having relatively small land areas between said outlet ports such that the openings of the inlet face are about 10 to 20 percent of the area of the inlet face and the outlet ports being to percent of the area of the outlet face, each passage having means for jet forming of stock flow in a first zone adjacent said inlet opening, each said passage widening gradually to a said outlet port, and each passage ofa vertical row of passages extending toward the slice at a different angle, the lowermost passage being in almost horizontal alignment with the slice and the uppermost passage extending at an angle less than 45, said downstream face being closely positioned to said slice to control turbulence in the outflow of the slice, inhibit fiber reflocculation and to avoid eddy current and cross-current flow in said flow between the distributor and slice.

2. An inlet according to claim 1 in which the openings are formed by arcuate land areas which are individual protrusions of the inlet face, and each opening has an internal shoulder serving to abruptly expand an inflowing stream to said distributor to create small scale turbulence in the stream.

3. An inlet according to claim 1 in which the overall passage length is between 8 and 16 inches, the distributor has an outlet face between about 2.5 to 4 inches in height, and the downstream face of the distributor is between about 5 and 12 inches away from such slice. 

1. An inlet for a papermaking machine comprising a pond type headbox, a slice and a pre-slice flow distributor communicating with said slice for directing a flow of paper-making stock from said headbox to said slice, said distributor having relative to said slice a large upstream inlet face and vertically disposed inlet openings, said inlet face of said distributor being convex on the side remote from said slice, a downstream outlet face small relative to said inlet face and larger than said slice and including outlet ports and a passage communicating each inlet opening with one outlet port, said downstream outlet face being arcuate in the same sense as the upstream inlet face, said upstream inlet face having relatively large land areas between said inlet openings and said downstream face having relatively small land areas between said outlet ports such that the openings of the inlet face are about 10 to 20 percent of the area of the inlet face and the outlet ports being 80 to 90 percent of the area of the outlet face, each passage having means for jet forming of stock flow in a first zone adjacent said inlet opening, each said passage widening gradually to a said outlet port, and each passage of a vertical row of passages extending toward the slice at a different angle, the lowermost passage being in almost horizontal alignment with the slice and the uppermost passage extending at an angle less than 45*, said downstream face being closely positioned to said slice to control turbulence in the outflow of the slice, inhibit fiber reflocculation and to avoid eddy current and cross-current flow in said flow between the distributor and slice.
 2. An inlet according to claim 1 in which the openings are formed by arcuate land areas which are individual protrusions of the inlet face, and each opening has an internal shoulder serving to abruptly expand an inflowing stream to said distributor to create small scale turbulence in the stream.
 3. An inlet according to claim 1 in which the overall passage length is between 8 and 16 inches, the distributor has an outlet face between about 2.5 to 4 inches in height, and the downstream face of the distributor is between about 5 and 12 inches away from such slice. 